Typical lithographic and offset printing techniques utilize plates that are permanently patterned, and are, therefore, useful only when printing a large number of copies of the same image, such as magazines, newspapers, and the like. Variable data digital lithography or digital offset lithographic printing has been developed as a system that uses a non-patterned re-imageable surface on an imaging member (printable blanket), which is initially uniformly coated with a dampening fluid layer. Regions of the dampening fluid are removed by exposure to a focused radiation source (e.g., a laser light source) to form pockets. A temporary pattern in the dampening fluid is thereby formed over the non-patterned re-imageable surface. Ink applied thereover is retained in the pockets formed by the removal of the dampening fluid. The inked surface is then brought into contact with a substrate, such as paper, plastic or metal, and the ink transfers from the pockets in the dampening fluid layer to the substrate. The dampening fluid may then be removed, a new uniform layer of dampening fluid applied to the re-imageable surface and the process repeated.
In order to meet digital offset printing requirements, the inks used with digital offset printing architectures typically should possess many desirable physical and chemical properties. The inks should be compatible with the materials it is in contact with, including the printing plate, the dampening fluid, the paper and the various rollers. The digital offset printing ink also should meet all functional requirements for transfer and curing.
Many black inks in the art, however, pose challenges when used with digital offset printing architecture. Such inks, usually formulated with carbon black, broadly absorb UV radiation and are inherently more difficult to cure than colored inks. High viscosity carbon black inks, which are best suitable for digital offset printing, are even more of a challenge since these printing processes may include the addition of rheology modifiers that further negatively impact the cure of carbon black inks. Moreover, carbon black inks are also capable of interacting with the carbon black containing blankets, resulting in transfer issues. High transfer efficiency is necessary for high resolution digital imaging. Accordingly, there remains a need in the art for black ink formulations that may be efficaciously used with digital offset printing.